We are Grow Architects, a team of Architects in Bristol that specialise in house alterations, extensions and loft conversions in easy travelling distance of surrounding areas Bath, Somerset and the South West.


We are here to guide you through the process but here are answers to some common questions

The Questions

What is planning permission?

Planning Permission, in simple terms, is asking if you can do a certain piece of building work. It will be granted (possibly subject to certain conditions) or refused.

Do I need planning permission?

Each project is different our advice can help to steer and support your project, from the planning stage through to completion.

For more information on whether your project will need planning, see the link below:


What is permitted development?

You can perform certain types of work without needing to apply for planning permission. These are called “permitted development rights”. In some areas of the country, known generally as ‘designated areas’, permitted development rights are more restricted or you may have had your rights withdrawn by the planning authority when they think the character of an area of importance would be threatened.

To find out more about whether you particular project may qualify for permitted development see the link below:


What is a Lawful Development Certificate?

While it should be possible in most cases to decide whether or not a proposed project qualifies as permitted development there will inevitably be instances where the decision is less clear cut. You may choose to apply for a lawful development certificate (LDC). This is not the same as planning permission but is proof that your household building work is lawful. We recommend applying for a LDC as it is very useful when it comes to selling your property and proving that a planning application was not necessary.

What are the building regulations and do I need to apply for approval?

Building regulations set standards for the design and construction of buildings to ensure the safety and health for people in or about those buildings. They also include requirements to ensure that fuel and power is conserved and facilities are provided for people, including those with disabilities, to access and move around inside buildings.

The following types of project amount to building work and will need building regulations approval:

  • The erection or extension of a building
  • An alteration involving work which will temporarily or permanently affect the ongoing compliance of the building, service or fitting with the requirements relating to structure, fire, or access to and use of buildings
  • Installing replacement windows using a builder or window company which is not FENSA registered
  • The installation or extension of a service or fitting which is controlled under the regulations
  • The insertion of insulation into a cavity wall
  • The underpinning of the foundations of a building
  • When you want to change the building’s fundamental use
  • Renovation of a thermal element
  • Change of a building’s energy status.

The Budget

How much will my building cost to build?

There are many factors involved in costing an extension project, from the size of the project right down to the quality of the paint you use on the walls. For a basic breakdown of average extension prices, follow these guidelines:

  • From £1,500per m² for basic construction work, up to £3,000 per m² for high-spec materials
  • If you’re adding bi-fold doors, allow £1,400to £1,800 per metre for these
  • Small extensions, under 15–20 square metres, have higher costs per square metre
  • Clay, peat, lots of nearby trees and sloping ground will all increase foundation costs
  • As a rough guideline, 50% of the budget will cover construction whilst the other 50% will cover the interior

As a very rough guide we would allow approximately £1700 per m2 for a project located in central Bristol. This figure can vary greatly depending on the location of the project, scope of works, size, whether it is above ground and specification (whether you have gold plated taps or not!).

How many builders should I approach for quotes?

We would recommend at least three. You must approach several builders and get full quotes for the proposed extension. Each builder will have different circumstances that will effect their quote, even though the materials and work won’t change. Approaching only one or two builders could give you an idea of a false average building cost.

The Process & Timescales

What is the process and how long will it take?

Step 1: Free initial consultation

We will visit you in your home and discuss in detail the alterations and updates you require. Following this meeting we will develop a fixed quote for the work to be undertaken.

Step 2: Measured Survey

We will take a measured survey and draw a computer model of your existing layout.

Step 3: Design development

Next we will develop some initial sketch ideas and layout options to discuss through with you.

Step 4: Planning submission (we take approx. 3 weeks to submission)

Once you are fully happy with the design if required we will submit a planning application to the local authority on your behalf.

Local authority planning decision time normally takes approx. 8 weeks.

Step 5: Building regulation drawings & specification  ( we take approx. 3 weeks to submission)

Additional information and drawings will be required to gain building control approval. During this stage we will also draw up a full specification to enable a builder to be able to price the works.

The drawings will then be submitted to the local authority of an approved independent inspector.

Additional information:

Throughout the process we will advise and explain any additional services you may require for example:

Party wall certificate,


Structural engineer,

Water board applications.